close
Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Sep 23;13(1):15897.
doi: 10.1038/s41598-023-43070-5.

Correlation between the presence of a cecal appendix and reduced diarrhea severity in primates: new insights into the presumed function of the appendix

Maxime K Collard #  1   2 , Jérémie Bardin #  3 , Bertille Marquet  4 , Michel Laurin  3 , Éric Ogier-Denis  5   6
Affiliations

Correlation between the presence of a cecal appendix and reduced diarrhea severity in primates: new insights into the presumed function of the appendix

Maxime K Collard et al. Sci Rep. .

Abstract

Increased severity or recurrence risk of some specific infectious diarrhea, such a salmonellosis or Clostridium difficile colitis, have been reported after an appendectomy in human patients. While several other mammals also possess an appendix, the suspected protective function against diarrhea conferred by this structure is known only in humans. From a retrospective collection of veterinary records of 1251 primates attributed to 45 species, including 13 species with an appendix and 32 without, we identified 2855 episodes of diarrhea, 13% of which were classified as severe diarrhea requiring a therapeutic medication or associated with a fatal issue. We identified a lower risk of severe diarrhea among primate species with an appendix, especially in the early part of life when the risk of diarrhea is maximal. Moreover, we observed a delayed onset of diarrhea and of severe diarrhea in species possessing an appendix. Interestingly, none of the primates with an appendix were diagnosed, treated or died of an acute appendicitis during the 20 years of veterinarian follow-up. These results clarify the function of the appendix among primates, as protection against diarrhea. This supports its presumed function in humans and is congruent with the existence of a selective advantage conferred by this structure.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Taxonomic distribution of the appendix in studied primate species. Subset of the phylogeny (tree n° 1 node-dated). Colors correspond to absence (black) and presence (red) of appendix. Solid circles refer to observed appendix presence or absence; empty circles correspond to inferred appendix presence or absence.
Figure 2
Figure 2
Incidence of diarrhea and severe diarrhea over the lifetime of primates with and without an appendix in the entire cohort. Appendix bearers experience their peak frequency of diarrhea later in life and suffer from fewer severe diarrhea episodes. The four curves represent the probability distributions (kernel density estimates) of the relative ages of diarrhea occurrences for individuals with an appendix (red) or without (black) and highlighting the severe diarrhea (dotted pattern; full color pattern includes all diarrhea). Diarrhea episodes have been equally sampled in individuals with, or without an appendix, regardless of their species. Ages have been standardized using average maximum longevity of each of the 45 species. Grey dots represent the number (nb) of diarrhea episodes divided by the number of individuals that have been observed in each time bin (right y-axis). This variable shows that the decreasing quantity of diarrhea throughout life is a genuine pattern.
Figure 3
Figure 3
Proportion of severe diarrhea among all diarrhea episodes of the entire cohort. Diarrhea episodes are less severe for individuals with an appendix during the first third of their life; after, the effect disappears and/or diarrhea are too scarce to quantify the effect. 1000 bootstrap sampling were performed in each of the four clades, then respectively averaged in clades without (Cercopithecoidea and Platyrrhini) and with (Lemuridae and Hominoidea) an appendix (Fig. 1). Dots and bars correspond to the mean and two standard deviations of the generated distributions (± 1 sd). This procedure was repeated in 14 time bins standardized by the maximal recorded longevity of each of the 45 species in our dataset. Numbers below correspond to the number of diarrheas in each of the four clades. Values above are p-values corresponding to the fraction of the bootstrap runs in which proportion of severe diarrhea is at least as high for individuals with an appendix as for individuals without an appendix. In the 14th time bin, an outlier (only one diarrhea recorded) has been moved to enhance legibility.
Figure 4
Figure 4
Flowchart representing the successive stages of the analysis in bootstrap sampling of diarrhea in the four clades to compare the severity of diarrhea over the lifespan of primates with and without appendix.
See this image and copyright information in PMC

References

    1. Smith H, Parker W, Kotzé S, Laurin M. Multiple independent appearances of the cecal appendix in mammalian evolution and an investigation of related ecological and anatomical factors. C.R. Palevol. 2013;12:339–354. doi: 10.1016/j.crpv.2012.12.001. - DOI
    1. Smith HF, et al. Comparative anatomy and phylogenetic distribution of the mammalian cecal appendix. J. Evol. Biol. 2009;22:1984–1999. doi: 10.1111/j.1420-9101.2009.01809.x. - DOI - PubMed
    1. Smith HF, Parker W, Kotzé SH, Laurin M. Morphological evolution of the mammalian cecum and cecal appendix. C.R. Palevol. 2017;16:39–57. doi: 10.1016/j.crpv.2016.06.001. - DOI
    1. Collard MK, Bardin J, Laurin M, Ogier-Denis E. The cecal appendix is correlated with greater maximal longevity in mammals. J. Anat. 2021;239:1157–1169. doi: 10.1111/joa.13501. - DOI - PMC - PubMed
    1. Smith HF. A review of the function and evolution of the cecal appendix. Anat. Rec. (Hoboken) 2023;306:972–982. doi: 10.1002/ar.24917. - DOI - PubMed

Publication types

LinkOut - more resources